Self-starting for dc motors

ABSTRACT

A noncommutating self-starting direct current motor having a magnetic rotor which turns through a position in which the motor field produces no driving torque on the rotor and a position in which the field produces maximum driving torque on the rotor, and positioning means for arresting the rotor in its maximum torque position when the motor field is turned off so as to condition the motor for automatic restarting when the field is restored.

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Lahde States Patent [72] Inventor: Reinhard N. Lahde, Los Altos, Calif.

[73] Assignee: Lockheed Aircraft Corporation, Burbank,

Calif.

[22] Filed: Nov. 14, 1969 [21] App]. No.: 876,757

[52] US. Cl. ..318/138,310/154,310/156,

[51] Int.Cl. ..11021: 29/00 [58] FieldofSearch ..310/163,41,181,154,156;318/138, 254

[56] References Cited UNITED STATES PATENTS 2,867,762 1/1959 Lehman eta1. ..318/254 1 Feb. 22, 1972 Primary Examiner-G. R. SimmonsAtt0rneyGeorge C. Sullivan and Ralph M. Flygare ABSTRACT Anoncommutating self-starting direct current motor having a magneticrotor which turns through a position in which the motor field producesno driving torque on the rotor and a position in which the fieldproduces maximum driving torque on the rotor, and positioning means forarresting the rotor in its maximum torque position when the motor fieldis turned off so as to condition the motor for automatic restarting whenthe field is restored.

9 Claims, 7 Drawing Figures A SWITCHING; 8 w h R EN lt; I j 42 44CIRCUIT l2 INVENTOR. REINHARD N. LAHDE Agent PATENTEDFEBZZ I972 3,644.809

sum 3 or 3 FIG..?

w WWWMR REINHARD N. LAHDE SELF-STARTIN G FOR DC MOTORS REFERENCE TOCOPENDING APPLICATIONS Reference is made herein to my copendingapplication Ser. No. 389,118, filed Aug. 12, I964, and entitled D. C.MO- TOR", now U.S. Pat. No. 3,541,407.

BACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates generally to motors and more particularly to a simplifiedself-starting direct current motor.

Prior Art Conventional direct current motors require a commutator, makeand break contacts, or some other mechanical switching mechanism forcontrolling current flow through the motor armature as the latter turns.Recently, transistorized switching circuits have been devised to performelectrically the switching function of the mechanical switchingmechanism required in the existing motors. My referenced patentdiscloses a simplified direct current motor of this type.

Briefly, my earlier motor has a magnetic rotor with circumferentiallyspaced north and south poles. About the rotor is a field structureincluding a coil to be energized with direct current to produce amagnetic field for turning the rotor. Connected to the field coil is atransistorized switching circuit which switches the field on and off inthe proper timing to cause continued rotation of the rotor. Thisswitching circuit is triggered between its on and off states by thevoltage induced in the field structure by the turning rotor. Onedisadvantage of my prior motor resides in the fact that it isself-starting only if the rotor is initially in a position wherein itsmagnetic poles are located in a plane transverse to the lines of forceof the motor field. In this position, a relatively large starting torqueis produced on the rotor when the field coil is energized by theswitching circuit. Assuming low bearing friction, the momentum acquiredby the rotor during its first 90 of rotation is sufficient to carry therotor through the following 180 of rotation, during which the motorfield is turned off, into the next power revolution. This initialrotation of the rotor actuates the switching circuit to continuerotation of the rotor. Under these conditions, then, the motor isself-starting.

On the other hand, if the rotor comes to rest with its magnetic poles ina plane generally parallel to the lines of the motor field, the fieldproduces no driving torque on the rotor or insufficient torque to startits rotation. In this case, the motor must be started manually by givingits rotor a slight spin. Under these conditions, then, the motor is notself-startmg.

SUMMARY OF THE INVENTION The present invention avoids the abovedisadvantage of my earlier direct current motor by providing the latterwith a positioning means for arresting its magnetic rotor in the properstarting position. It will be recognized from the earlier discussionthat this proper starting position is one in which the magnetic poles ofthe rotor are disposed in a plane transverse to the lines of the motorfield, such that this field, when energized, will produce a relativelylarge driving torque on the rotor. The initial rotation imparted to therotor by this starting torque activates the switching circuit of themotor to continue rotation of the rotor. A feature of one disclosedembodiment resides in means for inactivating the rotor positioning meanswhen the motor is started. This is desirable to reduce or eliminate, inthe starting and running phases of the motor, the positioning forceimposed on the rotor by the positioning means. Another feature of theinvention is concerned with various starting switch arrangements for themotor. At this point, it should be noted that while the invention willbe disclosed in connection with the direct current motor disclosed in myaforementioned patent, the invention is not limited in application tothis particular motor.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a self-starting DCmotor according to the invention equipped withmagnetic-rotor-positioning means;

FIG. 2 illustrates a modified self-starting motor equipped withmagnetic-rotor-positioning means and means for neutralizing the magneticfield of the positioning means during the starting phase of the motor;

FIG. 3 illustrates a further modified self-starting DC motor accordingto the invention;

FIG. 4 illustrates a self-starting DC motor according to the inventionequipped with rnechanical-rotor-positioning means;

FIG. 5 illustrates a self-starting motor according to the inventionembodying a starting circuit for initiating rotation of the rotor ineither direction of rotation;

FIG. 6 illustrates a self-starting motor embodying an alternativestarting circuit; and

FIG. 7 illustrates a self-starting motor embodying a further alternativestarting circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Turning first to FIG. 1, thereis illustrated a self-starting motor 10 according to the invention. Thismotor has a magnetic rotor 12 with diametrically opposed north and southpoles N, S. About the rotor 12 is a field structure 14 including a coil16. Coil 16 is energized from a DC power supply 18, in this instance abattery, through a switching circuit 20. Coil 16, when energized,produces a magnetic field between two magnetic poles 22, 24 of the fieldstructure I4. These magnetic poles are located at diametrically oppositesides of the rotor 12.

The switching circuit 20 is identical to that disclosed in my earliermentioned patent. Accordingly, there is no need to describe this circuitin explicit detail. Suffice it to say that the circuit includes a pairof transistors 26, 28 and three resistors 30, 32, and 34 which areconnected in the manner illustrated and balanced in a manner such thatthe circuit is activated by the voltages induced in the field coil 16 byrotation of the rotor 12 to switch the current flow through the coil offand on in the proper timed relation to cause continuous rotation of therotor 12. A switch 36 is placed between the power supply 18 and theswitching circuit 20 to permit starting and stopping of the motor.

The motor 10 described to this point is identical to that disclosed inmy earlier mentioned patent. As noted, this motor presents the inherentdisadvantage that it is self-starting only when the rotor 12 isinitially in its position of FIG. I or in a position 180 from theillustrated position. Thus, in each of these rotor positions, the rotorpoles N, S are disposed in a plane transverse to the lines of force ofthe motor field which exists between the magnetic poles 22, 24 of themotor field structure 14. Obviously, when the rotor is in this position,energizing of the field coil 16 produces a relatively large startingtorque on the rotor. Assuming relatively low bearing friction, theinitial spin imparted to the rotor by this starting torque is sufficientto activate the motor switching circuit 20. When thus activated, theswitching circuit periodically energizes the field coil 16 in the propertimed relation to continue rotation of the rotor.

Assume now that the rotor 12 comes to rest in a position spaced 90 fromthat illustrated in FIG. 1. In this case, the plane of the rotor polesN, S would then be generally parallel to the lines of force of the motorfield between its magnetic field poles 22, 24. Under these conditions,energizing of the field coil 16 would produce little if any drivingtorque on the rotor. Accordingly, it would be necessary to start themotor by hand by imparting an initial spin to the rotor.

According to the present invention, this disadvantage is avoided byproviding the motor 10 with positioning means 38 for always arrestingthe rotor 12 in the proper starting position, i.e., the position of FIG.1 or a position displaced I from the illustrated position. By thusarresting the rotor in the proper starting position, the motor obviouslybecomes selfstarting since initial energizing of the motor field coil 16will impart a sufficient spin to the rotor 12 to activate themotorswitching circuit 20 and thereby continue rotation of the rotor.The invention contemplates, within its scope, a variety of rotorpositioning means. In FIG. 1, for example, the rotor positioning means38 is a simple permanent magnet which is mounted in a stationaryposition with one pole of the magnet located close to the circumferenceof the rotor 12. In this instance, the north pole of the magnet islocated adjacent the rotor. Accordingly, the positioning magnet 38 iseffective to arrest the rotor 12 in its illustrated position, whereinthe south pole of the rotor is located directly opposite the north poleof the magnet.

It will be understood that the magnet 38 imposes a magnetic I centeringforce on the rotor 12 when the field coil 16 is deenergized so as tobring the rotor to rest in its illustrated starting position. While thiscentering action on the rotor is desirable during the stopping phase ofthe motor, it is undesirable during the starting phase of the motor.Thus, during the starting phase, the magnetic force on the rotor resiststhe initial spin which is imparted to the rotor by the motor field andis required to activate the switching circuit 20 for continuing rotationof the rotor. FIG. 2 illustrates an alternative rotor positioning means40 which avoids this problem. Positioning means 40 comprises a permanentrotor-positioning magnet 42 which is mounted in a stationary positionadjacent the rotor 12 to arrest the latter in its proper startingposition, as in the case of FIG. 1. Encircling the rotor end of thepositioning magnet 42 is a coil 44. This coil is connected in seriesbetween the motor switchingcircuit 20 and the motor field coil 16.Accordingly, the motor field coil 16 and the positioning magnet coil 44are energized concurrently. The magnet coil is wound in a direction suchthat current flow through this coil produces an electromagnetic fieldwhich opposes and thus tends to cancel the magnetic field of the rotorpositioning magnet 42. Preferably, the coil 44 is wound about amagnetically permeable tip 46 on the positioning magnet 42 in order toprevent demagnetization of the latter magnet by the coil.

From this description, it is evident that when the motor switch 36 isopened to stop the motor 10, the positioning magnet 42 becomes effectiveto arrest the rotor 12 in its proper starting position. When the switch36 is closed to start the motor, the magnetic field of the positioningmagnet 42 is at least partially neutralized by the magnetic field of thecoil 44, thereby reducing the magnetic force imposed on the rotor 12 bythe positioning magnet 42 during the starting phase of the motor.Obviously, the number of turns in the magnet coil 44 may be selected tovirtually eliminate all magnetic drag on the rotor.

Turning to FIG. 3, there is illustrated a modified direct current motorhaving an annular, ironless field structure 48 comprising a coil.Rotatably mounted within this coil, for turning about a diameter of thecoil, is a magnetic rotor 50 having north and south poles N, S. Themotor field coil 48 is energized through a transistorized switchingcircuit 20 in the same manner as the earlier described motors. In thiscase, the motor is provided with rotor positioning means 52 forarresting the rotor in the proper starting angle relative to the fieldcoil 48. The positioning means 52 comprise a pair of permanent barmagnets 54 disposed in planes parallel to the plane of the field coil 48and located at opposite sides of the spin axis of the rotor 50. Thesemagnets have their like poles adjacent one another. It will beunderstood by those versed in the art that the positioning means 52 iseffective to bring the rotor 50 to rest in the proper starting anglerelative to the field coil 48 when this coil is deenergized, thus tocondition the motor to restart automatically when the field coil isreenergized.

All of the rotor-positioning means described thus far are magneticmeans. FIG. 4 illustrates a modified direct current motor 56 equippedwith a mechanical rotor-positioning means 58. In this case, the rotor 60of the motor has a central shaft 62 supported in bearings 64 carried bya frame 66. Attached to one end of the rotor shaft 62 is a crank arm 68.A spring is connected between the outer end of this crank arm and theframe 66. About the rotor 60 is a field structure 70 like that embodiedin the motor of FIG. 3. This field structure is energized through aswitching circuit 20.

From this description, it is evident that when the motor 56 isdeenergized, the rotor-positioning spring 70 arrests the rotor 60 in apredetermined angular position. In this position, the north and southpoles of the rotor are disposed in the plane of the motor field coil.Accordingly, when the motor is energized, a starting torque is appliedto the rotor 60 for imparting an initial spin to the rotor for startingthe motor, as before.

It will be immediately evident to those versed in the art that a varietyof other mechanical rotor-positioning means may be employed in thepresent motor. FIG. 4 represents only one of these mechanical means.Other possible mechanical arrangements may comprise cams, detents, andvarious other mechanical configurations. If desired, themechanical-positioning means may be inactivated by centrifugal force, orin some other way, when the motor is energized so as to reduce oreliminate force or torque imposed on the rotor by the positioning means.

FIGS. 5 through 7 illustrate three alternative starting circuits for thepresent self-starting motor. The particular motor shown is equipped witha rotor-positioning magnet 38 like that in the motor of FIG. 1. However,it will become evident from the ensuing description that the startingcircuits of FIGS. 5 through 7 may be used, as well, with any of thedescribed selfstarting motor configurations of the invention. Thestarting circuit 74 of FIG. 5 includes a pair of switching circuits 20a,20b connected in electrical parallel to the motor coil 16 and energizedfrom DC power supplies 18a, 18b through starting switches 36a, 36b. Theterminals of the power supplies are reversed. Starting circuit 20a isidentical to the starting circuit 20 discussed earlier; starting circuit20b differs only in that a PNP-transistor is used instead of an NPN, andvice versa, in accordance with the reversed direction of current flow incorresponding parts of the circuit. Accordingly, it will be understoodthat closing of the switch 36a starts the motor 10 in one direction ofrotation and closing of the switch 36b starts the motor in the oppositedirection of rotation.

The starting circuit of FIG. 6 has a switching circuit 20, a condenser76 connected in electrical series with a charging resistor 78 across theDC power supply 18, and a starting switch 80. In the normal runningposition of the switch, shown in full lines in FIG. 6, the switchcontacts 80a, 80b, 80c are closed to connect the input of the switchingcircuit 20 to the power supply 18 and the output of the switchingcircuit to the motor field coil 16. The motor 10 is then conditioned forrunning in the manner explained earlier. In the starting position of theswitch 80, shown in broken lines, the switch disconnects the switchingcircuit 20 from both the motor 10 and the power supply 18 and connectsthe starting condenser 76 across the motor coil 16. The condenser thendischarges through the coil to start the motor 10. The switch 80 must bereturned to its running position before the rotor 12 of the motor comesto rest following the initial spin imparted to the roller by thecondenser charge.

The starting circuit of FIG. 7 has a switching circuit 20, a startingcondenser 76, a charging resistor 78, and a starting switch 80 arrangedin essentially the same manner as in the starting circuit of FIG. 6. Inaddition to these circuit elements, however, the starting circuit ofFIG. 7 is equipped with a reversing switch 82 which may be set todischarge the condenser 76 in either direction through the motor fieldcoil 16 when the starting switch 80 is closed to its starting position.The starting circuit of FIG. 7, therefore, permits starting of the motor10 in either direction of rotation.

While the present invention has been disclosed in connection with thetwo-pole motor of my aforementioned patent, it will be understood thatthe invention may be utilized, as well, with any of the multiple polemotors disclosed in the said patent. Moreover, the rotor positioningmeans of the invention may conceivably be utilized to advantage on othertypes of direct current motors.

What is claimed as new in support of Letters Patent is:

l. A self-starting direct current motor comprising:

a magnetic rotor having circumferentially spaced north and south poles,

an ironless electromagnetic field structure comprising a coil uniformlyspaced from said rotor and adapted to be intermittently energized bydirect current to produce an intermittent magnetic field forcontinuously rotating said rotor,

said rotor being rotatable through a starting position wherein saidintermittent magnetic field produces a relatively large driving torqueon said rotor, and

rotor-positioning means spaced apart from said field structure forarresting said rotor in said starting position when said field structureis deenergized.

2. A motor according to claim 1 wherein:

said motor-positioning means comprises magnetic means coacting with thefield of said rotor so as to statically orient said rotor in saidstarting position.

3. A motor according to claim 1 wherein:

said motor includes a frame supporting said rotor, and

said rotor-positioning means comprises mechanical indexing meansoperatively connected between said rotor and 1 tioning means comprises:

a permanent magnet having a magnetically permeable tip extending fromone pole thereof;

a bucking coil wound on said permanent magnet intermediate the polesthereof in a manner such that when said coil is energized with a directcurrent it will produce a magnetic field which at least partiallynullifies the field of said permanent magnet; and

means for intermittently energizing said bucking coil concurrently withenergization of said electromagnetic field structure.

6. A self-startin g brushless direct current motor comprising:

a magnetic rotor having circumferentially spaced north and south poles,

an ironless electromagnetic field structure comprising a coil adapted tobe intermittently energized by direct current to produce an intermittentmagnetic field for continuously rotating said rotor, and wherein thespacing between said coil and said rotor remains uniform during rotationof said rotor;

a switching circuit connected to said coil for regulating current flowthrough said coil in response to rotation of said rotor in such a manneras to cause continuous rotation of said rotor, said rotor beingrotatable through a starting position wherein said rotor poles areoriented in self-starting relation to said magnetic field structure toproduce a relatively large driving torque on said rotor; and

magnetic means coacting with the poles of said rotor, and spaced apartfrom said field structure for arresting said rotor in said startingposition when said coil is deenergized.

7. A motor according to claim 6 wherein:

said magnetic means comprises a permanent magnet having one poleadjacent said rotor.

8. A motor according to claim 7 wherein said rotor-positioning meanscomprises:

a permanent magnet having a magnetically permeable tip extending fromone pole thereof and adjacent said rotor;

a bucking coil surrounding said magnet in a manner such that energizingof said coil with a direct current produces a magnetic field which atleast partially nullifies the magnetic field of said magnet; and, meansfor energizing said bucking coil concurrently with energization of saidfield structure.

9. A self-starting brushless direct current motor comprising:

a magnetic rotor having circumferentially spaced north and south poles;

an electromagnetic field structure about said rotor including a coiladapted to be intermittently energized by direct current to produce anintermittent magnetic field for continuously rotating said rotor;

a switching circuit connected to said coil for regulating current flowthrough said coil in response to rotation of said rotor in such a manneras to cause continuous rotation of said rotor, said rotor beingrotatable through a starting position wherein said rotor poles areoriented in self-starting relation to said magnetic field to produce arelatively large driving torque on said rotor;

starting means for said motor including a pair of terminals forconnection to a DC-power source, a condenser, and switch means forselectively connecting said terminals to said switching circuit andcondenser for selectively energizing said circuit and charging saidcondenser, and disconnecting said switching circuit from said field coiland terminals and discharging said condenser through said coil toinitiate rotation of said motor, said switch means including means forselectively discharging said condenser in either direction through saidfield coil to initiate rotation of said rotor in either direction; and

magnetic means coacting with the poles of said rotor for arresting saidrotor in said starting position when said coil is deenergized.

1. A self-starting direct current motor comprising: a magnetic rotorhaving circumferentially spaced north and south poles, an ironlesselectromagnetic field structure comprising a coil uniformly spaced fromsaid rotor and adapted to be intermittently energized by direct currentto produce an intermittent magnetic field for continuously rotating saidrotor, said rotor being rotatable through a starting position whereinsaid intermittent magnetic field produces a relatively large drivingtorque on said rotor, and rotor-positioning means spaced apart from saidfield structure for arresting said rotor in said starting position whensaid field structure is deenergized.
 2. A motor according to claim 1wherein: said motor-positioning means comprises magnetic means coactingwith the field of said rotor so as to statically orient said rotor insaid starting position.
 3. A motor according to claim 1 wherein: saidmotor includes a frame supporting said rotor, and said rotor-positioningmeans comprises mechanical indexing means operatively connected betweensaid rotor and frame.
 4. A motor according to claim 1 wherein: saidrotor-positioning means comprises a permanent magnet having one poleadjacent said rotor and coacting therewith so as to statically orientsaid rotor in said starting position.
 5. A motor according to claim 1wherein said rotor-positioning means comprises: a permanent magnethaving a magnetically permeable tip extending from one pole thereof; abucking coil wound on said permanent magnet intermediate the pOlesthereof in a manner such that when said coil is energized with a directcurrent it will produce a magnetic field which at least partiallynullifies the field of said permanent magnet; and means forintermittently energizing said bucking coil concurrently withenergization of said electromagnetic field structure.
 6. A self-startingbrushless direct current motor comprising: a magnetic rotor havingcircumferentially spaced north and south poles, an ironlesselectromagnetic field structure comprising a coil adapted to beintermittently energized by direct current to produce an intermittentmagnetic field for continuously rotating said rotor, and wherein thespacing between said coil and said rotor remains uniform during rotationof said rotor; a switching circuit connected to said coil for regulatingcurrent flow through said coil in response to rotation of said rotor insuch a manner as to cause continuous rotation of said rotor, said rotorbeing rotatable through a starting position wherein said rotor poles areoriented in self-starting relation to said magnetic field structure toproduce a relatively large driving torque on said rotor; and magneticmeans coacting with the poles of said rotor, and spaced apart from saidfield structure for arresting said rotor in said starting position whensaid coil is deenergized.
 7. A motor according to claim 6 wherein: saidmagnetic means comprises a permanent magnet having one pole adjacentsaid rotor.
 8. A motor according to claim 7 wherein saidrotor-positioning means comprises: a permanent magnet having amagnetically permeable tip extending from one pole thereof and adjacentsaid rotor; a bucking coil surrounding said magnet in a manner such thatenergizing of said coil with a direct current produces a magnetic fieldwhich at least partially nullifies the magnetic field of said magnet;and, means for energizing said bucking coil concurrently withenergization of said field structure.
 9. A self-starting brushlessdirect current motor comprising: a magnetic rotor havingcircumferentially spaced north and south poles; an electromagnetic fieldstructure about said rotor including a coil adapted to be intermittentlyenergized by direct current to produce an intermittent magnetic fieldfor continuously rotating said rotor; a switching circuit connected tosaid coil for regulating current flow through said coil in response torotation of said rotor in such a manner as to cause continuous rotationof said rotor, said rotor being rotatable through a starting positionwherein said rotor poles are oriented in self-starting relation to saidmagnetic field to produce a relatively large driving torque on saidrotor; starting means for said motor including a pair of terminals forconnection to a DC-power source, a condenser, and switch means forselectively connecting said terminals to said switching circuit andcondenser for selectively energizing said circuit and charging saidcondenser, and disconnecting said switching circuit from said field coiland terminals and discharging said condenser through said coil toinitiate rotation of said motor, said switch means including means forselectively discharging said condenser in either direction through saidfield coil to initiate rotation of said rotor in either direction; andmagnetic means coacting with the poles of said rotor for arresting saidrotor in said starting position when said coil is deenergized.